Development of direct hydrocarbon solid oxide fuel cells with enhanced stability and performance
In this dissertation, solid oxide fuel cell (SOFC) electrodes for the direct utilization of hydrocarbon fuels with increased thermal stability and high-performance were developed. The work includes creating novel microstructures in metallic-based anodes as a means to enhance the thermal stability of Cu-based anodes, developing a strategy for obtaining high-performance in ceramic-based anodes, and designing high-performance ceramic anodes that can maintain thermal stability. Bimetallic structures that would exhibit the carbon tolerance of Cu and the thermal stability of a more refractory metal were studied. The two systems investigated were Cu-Cr and Cu-Co, where the Cr and Co were integrated into the electrode by electrodeposition onto Cu-based anodes. The Cu-Cr system demonstrated enhanced thermal stability in dry H2; however, exposure to H2-H2O mixtures resulted in complete oxidation of Cr and loss of enhanced thermal stability. The Cu-Co system dramatically enhanced thermal stability in humidified H2 (3% H2O) and was shown to be stable in dry CH4, despite the tendency for Co to catalyze the formation of carbon fibers in the presence of hydrocarbons. It was shown that Cu migrates to the surface of the Co upon heating above 873 K, forming a chemically stable Cu layer that appears to be approximately one monolayer thick. A proposal that high SOFC anode performance can be achieved by using a very thin, catalytically active functional layer with a non-catalytic conduction layer was tested. Excellent performance and relatively good thermal stability was demonstrated with a functional layer impregnated with 40 wt% Ce02 and 1 wt% Pd into YSZ. The functional layer design demonstrated that materials with relatively low electronic conductivity can be used in the anode if the functional layer is thin enough. The addition of dopant levels of catalytic metals was found to be critical. Pd exhibited the best performance in H 2, while Pd and Cu showed similar performance in n-butane. In an attempt to create more thermally stable electronic conductivity in ceramic-based functional layers, porous backbones consisting of a physical mixture of La0.3Sr0.7TiO3 (LST) and YSZ were prepared. The approach appears very promising for achieving stable electronic conductivity in the functional layer.
Gross, Michael D, "Development of direct hydrocarbon solid oxide fuel cells with enhanced stability and performance" (2007). Dissertations available from ProQuest. AAI3271759.